The verse has quite a few apocalyptic monsters, including a group literally called "Beasts":
- First, there's the seven Evils of Humanity, who all manifest under the Beast class. Each of them is capable of bringing about the End of the World as We Know It by themselves and the appearance of one generally means that multiple Godzilla Thresholds will need to be crossed to bring them down. While their forms and nature vary, a few of them are literal beasts of armageddon.
- The first of the Beasts the heroes encounter is Beast II, aka Tiamat, the Mesopotamian goddess of chaos and representing the law of "Retrogression", who wants to return all life on Earth back to its primordial state. Her mindset is utterly alien to humans and her mentality runs solely on three things: Wanting to be the mother of all life again, slaughtering humanity and anything that can stop her from achieving that, and subconsciously holding back her full power because on some level she still loves humanity as a mother does, so she limits herself to "just" throwing her monsters and Chaos Tide rather than using her own physical power as much as possible.
- The Final Singularity reveals that the Big Bad responsible for the Incineration of Man is actually Beast I, a Mind Hive of the demons of the Ars Goetia inhabiting Solomon's body (actually called Goetia) representing the law of "Pity". Unlike most examples of this trope, Goetia is a Well-Intentioned Extremist whose ultimate goal is to Restart the World and eliminate all human suffering.
- Beast III is actually two separate entities representing different aspects of "Pleasure", who are diametrically opposed to one another (and also hate each other's guts).
- Beast III/R, representing Lust, is an alternate version of Sessyoin Kiara that was corrupted by the Demon Pillar Zepar into becoming more like her Moon Cell counterpart and sought to merge with the Earth itself.
- Beast III/L, representing Depravity, is a composite of Kama and Mara inhabiting Dark Sakura as a vessel. Interestingly, her manifestation is due to events going on in the Lostbelts - normally Kama is in control of the Psuedo-Servant, but because of Arjuna Over Gods fusing with the Hindu pantheon, the gods that kept Mara in check no longer existed and she manifested as a Beast.
- Beast IV is none other than Fou, the little magical animal that accompanies the heroes on their adventures. As it turns out, Fou is a premature form of Primate Murder, a monster whose entire purpose is to slaughter all of humanity and represents the law of "Comparison". Thankfully, Fou's time with the heroes has caused him to undergo a Heel–Face Turn before maturing, and he sacrifices his future power for the sake of resurrecting Mash, effectively putting an end to Primate Murder before it even appears.
- Beast VI is the Beast of Revelations itself, who Arthur Pendragon has been hunting across the multiverse after failing to finish it off for good in Fate/Prototype.
- It's heavily implied that Tamamo-no-Mae has the potential to become a Beast in her Nine-tailed state.
- Koyanskaya/Tamamo Vitch's ultimate goal is to become a new Evil of Humanity of her own in the vein of Amaterasu, Tamamo's original self. When confronting her in Olympus, she's fought as the "Prized Beast" and manifests as a mass of shadows vaguely shaped like a multi-tailed fox. In her Reality Marble manifested in her homeland of Tunguska, she succeeds in becoming an alternate Beast IV, taking on a twisted chimeric form from absorbing various beasts of the Lostbelts similar to the evil fox spirit Daji representing the law of "Cherishment". While her transformation was incomplete due to outside factors, Koyanskaya of Darkness' Noble Phantasm shows the "Prized Beast's" true form as a pure white fox with multiple tails and eyes (and eyes on the tails) wreathed in sunfire.
- Beast VII is only mentioned in passing at the end of the Final Singularity, but its alternate titles, "The VII of the End" and "Beast that Announces the End" implies it to be the final Evil that will bring about the End of the World as We Know It once and for all. The end of Olympus reveals its identity: the Foreign God, aka U-Olga Marie, the Big Bad of Part 2 responsible for the Lostbelts. However, as the end of Lostbelt 7 reveals, she isn't even the Big Bad and is just merely one of the servants of the true masterminds, Marisbury Animusphere and CHALDEAS.
- An alternate version of Beast I appears in Lostbelt 7, Camazotz, a Mayan bat god who represents Oblivion, as in being forgotten. Ironically, he became a Beast specifically to stop another apocalyptic destroyer, the Ultimate One known as ORT who was destroying the ancient human civilization of the Lostbelt he was the king of, but it came at cost of the sacrifice of all his human subjects to empower him plus millions of years locked in a Forever War with the alien before he subdued it, and the thought that the heroes will destroy the Lostbelt he lives in and erase all his people's accomplishments caused him to snap and try to destroy them.
- The Arcade version of the Grand Order introduces an Alternate Self of Beast VI, Queen Draco, aka the Whore of Babylon or the Mother Harlot, who is also an alternate self of Nero. In this version of the game, she replaces Goetia as the Big Bad of Part 1. She is ironically opposed by Tiamat, who made a Heel–Face Turn after being defeated by the heroes in the main game and now doesn't want the world the heroes worked so hard to save to be destroyed.
- While he doesn't possess the Beast Class, Surtr in Lostbelt 2 qualifies. Initially he played the same role he did in Norse Mythology, but decided to Screw Destiny by destroying everything rather than just ending the Norse Age of Gods, consuming Fenrir and threatening to spread Ragnarok to the rest of the world. He was eventually sealed, but the damage was done, and his timeline was pruned. Unfortunately, Ophelia accidentally made contact with him via her Mystic Eye, allowing him to be summoned in Sigurd's body when she became a Crypter, and eventually leading to his true body being released.
- Angra Mainyu, if succesfully incarnated, would have been reborn as the Beast of Retribution. He drives the plot of Fate/Zero and its sequels.
- Likewise, the Calamities serve this purpose in Lostbelt 6. As a world where the Human Order no longer has influence, they are periodically formed from the sins of the land's fairy inhabitants, and from the land itself in an attempt to abort its world's unnatural existence. The Great Calamity two thousand years ago actually succeeded in a previous timeline, and the present-day Calamities destroy the Lostbelt again, nearly followed by the entire planet. Of the Calamities shown or referenced:
- The King of the Mors was a powerful entity that possessed the power to forcibly corrupt faeries into Mors at a rapid rate and plunged Faerie Britain into a massive war for survival as his path reduced the lands he traveled through to lifelessness. He was only barely beaten but would eventually reincarnate to try again.
- The Caterpillar Wars was an event where legions of caterpillar-shaped Mors began to appear and attack Faerie Britain en-masse. While that might not sound threatening, the Lostbelt Queen Morgan has a crippling phobia of insects and more or less sat out on dealing with them, which required the faerie who would become Faerie Knight Gawain to step up as the hero who would defeat them.
- The Calamity of Resurrection, otherwise known as the "Darlington zombie incident", was a city-wide Zombie Apocalypse that wiped out almost all of the inhabitants of Darlington before it was stopped. It was caused by Darlington's lord Grimalkin forcing the faerie Baobhan Sith into feeding on the blood of corpses until they rose again seemingly entirely out of self-serving curiosity. Morgan established New Darlington to replace it and made the newly-appointed Faerie Knight Tristan aka Baobhan Sith its new lord.
- The Calamity of Norwich is a massive shadow with "arms" of stone with eyes inside them, and it's so-named because it's predicted its arrival would herald the destruction of the city of Norwich. While it's defeated by Chaldea, it's later revealed it was actually the compressed form of Curses spread by the Great Calamity Cernunnos, and countless more of them appear when Cernunnos awakens later on.
- The Calamity of Flame is the true form of Faerie Knight Lancelot, otherwise known as Melusine and in reality the sentient left hand of the primordial dragon Albion, destined to become a second Albion and lay waste to Faerie Britain in criss-crossing firestorms from the heavens. While she was able to fight off her transformation thanks to being named Melusine, events eventually conspire to force her to give up that and surrender to her inner nature.
- The Calamity of the Beast is the true form of Faerie Knight Gawain, otherwise known as Black Dog Barghest who is destined to become a rampaging beast that devours all that stands in her path and drown Britain in fire and lightning. While she sought to temper her predatory instincts, in the end crossing the Despair Event Horizon at realizing she both failed to do so and that the humans and faeries she wanted to protect were either murdered or proved to be monstrous backstabbers causes her to give in to her inner beast and hope Chaldea can give her a Mercy Kill.
- The Calamity of Curses is the body of the ancient dead god Cernunnos, whose murder by the original six faeries helped create the land of Faerie Britain and now animated by the accumulated curses of the dead god's lingering emotions and the constant sins of the faeries. Awakened by the cursed soul of Fairy Knight Tristan, he rises from the Great Pit and spreads out his collected curses that not only start destroying the lands and killing with their sheer potency, they also start causing faeries to turn into Mors almost spontaneously, and these curses threaten to spread to the rest of the planet.
- The Abyssal Wyrm is the true power of Oberon Vortigern, the reincarnated King of the Mors who after the death of Cernunnos is able to manifest a massive Draconic Abomination of darkness nearly the size of Faerie Britain itself, which he proceeds to use to suck the shattered remnants of the island into a Bottomless Pit and threatens to turn it on the rest of the planet.
